Do I need to worry about black snakes?

Hi - I don't yet have chickens but am educating myself on how to create as safe as possible environment from the start. We have black snakes (and others) in North Carolina. Last year I rescued a baby bird but a snake crawled through the doggie door into the cage I kept on my screened porch, and the bird was gone without a trace. Next day one of my dogs killed the snake, and the cycle of life continues...

Anyhow, I've seen things on the web concerning snakes eating a full sized chicken. How serious is the threat and what do you do to prevent it. A wire cage locked at night wouldn't work. Would have to be complete containment with no small space for a snake to slither through. Suggestions?